CR (Cognitive Radio) is a method for overcoming spectrum resource shortage effectively in the prior art. Through spectrum sensing, the CR technology obtains and accesses unused authorized bands on a precondition that no intra-frequency interference is caused to authorized users and the adjacent-frequency interference is not too high. OFDM (Orthogonal Frequency Division Multiplexing) simply and efficiently suppresses ISI (Inter-Symbol Interference) caused by channel time dispersion and implements high-speed data transmission. The OFDM technology divides a signal bandwidth that suffers selective fading of channel frequency into several mutually orthogonal subcarriers with flat fading, and reduces complexity of signal detection on the receiver; the number of subcarriers may be changed to obtain different bandwidths and adapt to variable-bandwidth operations; the subcarriers are allocated to different users, and multi-user access is implemented in an OFDMA mode, and even OFDM transmission can be implemented on discontinuous bands. However, the OFDM is defective in slow attenuation of outband radiation, and causes great outband interference to authorized users.
There are two methods for overcoming the outband interference in the prior art. The first method is to use AIC (Active Interference Cancellation) and AST (Adaptive Symbol Transition) to calculate current transmitted data blocks, and insert interference cancellation subcarriers or symbol extensions to suppress outband interference, but this method is too complicated because it requires calculation of each data block. The second method is to apply subcarrier weighting, namely, multiply the OFDM subcarrier by a corresponding weighting factor directly to suppress outband interference, but the calculation load is too heavy in this method because the current weighting factor needs to be worked out according to each data block respectively.
The methods for suppressing outband interference in the prior art can suppress outband interference to some extent, but are very complicated and require a heavy load of calculation.